Glucose as a fuel molecule Flashcards
What is glucose?
Glucose is a common fuel molecule - all organisms can use glucose as fuel
Glucose is oxidised in glycolysis - glycolysis is usually cytoplasmic in eukaryotes, in mammals all cells can use glucose in glycolysis
All other pathways that use molecules fuel occur in the mitochondria whereas glycolysis occurs in the cytoplasm
What happens when RBC develop?
As red blood cells develop they lose lots of organelles including mitochondria hence RBC rely on glycolysis for fuel as they do not have a mitochondria, however have a cytoplasm
Why is glucose a preferred fuel molecule?
Glucose is the preferred fuel in the brain - uses around 120g of glucose per day
The brain uses glucose rather than other sources for fuels as a high level of fatty acid metabolism is dangerous due to relying on mitochondrial reactions and higher levels of oxygen which risks anoxia and higher production of damaging oxygen species hence using glucose is ‘safe’
Why is glucose favoured as a fuel molecule in the eye?
Glucose is favoured in the eye as it can make ATP in the cytoplasm with low levels of oxygen
There is not many blood vessels nor mitochondria in our eyes, this is because if we had lots the light may be refracted which would affect our vision
What do red and white muscle cells use for fuel?
Red muscle uses fat as fuel, used under aerobic conditions, has a good supply of oxygen, lots of mitochondria
White muscle uses glucose as fuel, used for short periods of time, less access to oxygen, anaerobic conditions, does glycolysis so it can use glucose as a fuel in cytoplasm
What is glycolysis?
Glycolysis is the splitting of glucose
It is the conversion of one molecule of glucose (6 carbons) to two molecules of pyruvate (3 carbons)
Energy is conserved in ATP and NADH
Pyruvate may be further metabolised aerobically or anaerobically
What are the two phases of glycolysis?
In the first phase, energy investment phase, the energy needs to be invested into the fuel molecule so that we can extract the energy back out - requires an energy input (2 ATP hydrolysed to 2 ADP to activate glucose)
Second phase is where we make an ATP profit, we use 4 ATP hence we profit 2ATP in this reaction
2 NAD+ are reduced to 2 NADH
2 Pyruvate is produced as a product (contains carbon dioxide)
Why do we split the glucose molecule?
Splitting the glucose molecule occurs at the end of the investment phase, after a conversion both 3-carbon molecules are processed in the same way
Set of reactions after splitting glucose occur twice per each molecule which allows us to make 4ATP
How is glucose converted to glucose-6-phosphate?
Glucose -> G6P reaction is catalysed by hexokinase, glucose is taken and a phosphate is added onto it, for this to occur hexokinase needs to be coupled with ATP
How is glucose-6-phosphate converted to fructose-6-phosphate?
G6P -> F6P is just a rearrangement, driven forward in pathway as not standard conditions
∆G˚=+1.6 occurs when you have 1 mol of G6P and 1 mol of F6P, in the cell we do not have these concentrations hence the reaction can occur
How is fructose-6-phosphate converted to fructose-1,6-biphosphate?
F6P -> FBP is where we add another phosphate which is energetically unfavourable however it is coupled to ATP hydrolysis hence the overall reaction is energetically favourable
What is the splitting/aldolase reaction?
Splitting reactions occurs - aldolase splits the FBP into two 3-carbon 1 phosphate molecules (DHAP and G3P)
G3P is used in the energy payoff phase which keeps concentration low and drives reaction DHAP -> G3P
Reaction between DHAP to G3P is a reaction that can occur in both directions as DHAP concentration is higher, however it is driven in the DHAP -> G3P direction due to the rearrangement of G3P
What is substrate level phosphorylation?
The direct use of energy from a substrate molecule to drive the synthesis of ATP
One way to release the energy to drive a substrate level phosphorylation is the cleavage of a high-energy phosphate ester bond on a substrate
What does the oxidation of G3P do?
Key reaction for making an ATP profit is the oxidation of glyceraldehyde-3-phosphate
G3P is oxidised to 1,3-BPG - this allows us to do two substrate level phosphorylations
NAD+ is reduced providing oxidising power and phosphate from solution is added to substrate. The addition of phosphate is powered by oxidation of G3P, does not require ATP
How is phosphogylcerate kinase involved in reaction of 1,3-BPG to 3PG?
Phosphogylcerate kinase cleaves phosphate that releases energy from 1,3-BPG to make 3PG which releases ATP as the phosphate is transferred from 1,3-BPG to ATP
